The invention relates to a swing-arm arrangement for moving and positioning at least one magnetic head over at least one surface of at least one rotatable rigid magnetic disc of a magnetic-disc storage apparatus for the storage and reproduction of data in digital form, which arrangement comprises: at least one swing arm which is pivotable about a pivotal axis, the swing arms, if there is a plurality of such arms, being spaced from each other and being stacked to form an assembly of swing arms, which assembly is pivotable about said pivotal axis; at least one flat control coil which is connected to the swing arm or to the swing-arm assembly, the control coils, if there is a plurality of such coils, being stacked to form an assembly of control coils which are spaced from each other; a permanent magnetic stator, comprising: a stator frame, flat, axially magnetized permanent stator magnets, which are connected to the stator frame and between which air gaps are formed for each flat control coil, so that each control coil is movable in an axial permanent magnetic field within an air gap between permanent stator magnets, and an iron stator end-plate on each side of the stator, which stator end-plates extend over the interposed control coils and stator magnets and on which the outermost stator magnets are mounted, so that the axial permanent magnetic stator fields are closed via the iron stator end-plates; and a bearing arrangement for pivotably journalling the swing arm or swing-arm assembly, which bearing arrangement comprises two ball-bearings, each having an inner race and an outer race, and a pivotal bearing pin on which both the swing arm or swing-arm assembly and the inner races of the two ball-bearings are mounted.
Magnetic disc storage equipment, comprising one or a plurality of rigid magnetic discs, which each serve for the storage and reproduction of data in digital form on at least one side and generally on both sides, is employed on a large scale as peripheral equipment for data processing apparatus such as computers.
The magnetic discs rotate with a high speed, for example 3600 revolutions per minute, and the magnetic heads, which are secured to the ends of the carrying-arm arrangements, are moved over the surfaces of the magnetic discs to locations which are preselected by the data processing apparatus in order to store data in a specific track on the magnetic disc or in order to reproduce data from said track. The carrying-arm arrangements comprise carrying arms which are either linearly movable in a radical direction or which are pivotable about a pivotal axis parallel to the axis of rotation of the magnetic discs. The invention relates to a carrying arm arrangement of the last-mentioned type, herein referred to as a swing-arm arrangement. The magnetic heads should be moved as fast as possible over the magnetic discs in order to minimize the time required for locating the correct track and storing or reproducing the data. The magnetic discs are manufactured with an extremely high degree of flatness. The magnetic heads float on a very thin film of air very close to the surfaces of the magnetic discs.
In many cases each magnetic head is secured to a resilient magnetic head carrier in order to obtain the mobility which permits the magnetic head to float on the air film and in order to provide a resilient load which exerts an accurately defined pressure on said head. In order to minimize the external dimensions of magnetic-disc storage equipment, the various manufacturers attempt to arrange the magnetic discs as close as possible to each other. The carrying-arm arrangements, especially when they are interposed between two magnetic discs, should therefore be as flat as possible and move as close as possible to the magnetic-disc surface. It is obvious that the carrying arm should never touch the magnetic disc surface, because this would render the magnetic disc unserviceable.
Carrying-arm arrangements for magnetic-disc storage equipment should therefore be manufactured with the necessary precision.
A swing-arm arrangement of the type mentioned in the opening paragraph is known from U.S. Pat. No. 4,150,407. The known swing arm arrangement comprises one or more aluminium swing arms in the form of bifurcated levers which are pivotable about a pivotal axis disposed between two ends. Arranged near the one end of each swing arm is a magnetic head unit comprising the magnetic head and a resilient magnetic head carrier, which carrier is rigidly connected to the carrying arm. On the other end of the swing arm a control coil is arranged. Said coil belongs to electromagnetically and electrically controllable actuating means by means of which it is possible to impart a pivotal movement about the pivotal axis of the swing arm to said arm, so as to enable the magnetic head to be moved over the magnetic disc in a substantially radial direction.
In a version comprising a plurality of swing arms, said arms are arranged above and spaced from one another and they are combined to form an assembly of swing arms which are pivotable about the pivotal axis. Each swing arm carries a separate flat control coil, so that these coils are also combined to form an assembly of control coils which are spaced from each other. The assembly of swing arms is journalled on a frame by means of a bearing arrangement, which comprises two ball-bearings and a bearing pin on which the the inner races of the ball bearing are fixed by suitable means so as to be axially spaced from each other. The outer races of the ball-bearings are fitted in a bearing housing which is screwed to the deck of the magnetic-disc storage apparatus, a compression spring between the outer races eliminating the axial bearing play. The control coils move in a permanent magnetic stator. Said stator comprises a stator frame and a plurality of flat, axially magnetized permanent stator magnets, which are connected to the stator frame and between which air gaps are formed for each flat control coil, so that each control coil is movable in an axial permanent magnetic field within an air gap between permanent stator magnets. On each side of the stator, iron stator end plates are arranged which extend over the interposed control coils and stator magnets and on which the outermost stator magnets are mounted, so that the axial permanent magnetic stator fields are closed via the iron stator end plates. Each control coil comprises turns of an electrically conductive material wound onto a plastics coil former, which forms one structural unit with the control coil by means of a synthetic resin. The control coils are connected to the swing arms by clamping and gluing, on the ends of the swing arms which are remote from the magnetic heads.
The magnetic heads are moved over the magnetic discs with a high speed in a substantially diametrical direction, in order to minimize the time required for locating a track and storing or reproducing the data. Thus, the swing arm or swing-arm assembly is moved with jerky movements, which give rise to relatively great inertial forces. The bearing arrangement should therefore be robust and stable.